No, the difference is that cats are kept as a fun companion. It's a choice. The choice of killing yourself is a bit different I'd say. That's a false comparison.

I'm not advocating for anyone to have or not have cats because of the environment. There's no problem with any single individual cat, just like there is no problem with an individual owning a car. It is every household having one that is causing problems. But no one is going to forbid a certain individual from owning a car, neither am I judging anyone for owning a cat.

For a choice of having a pet it's worth considering the effect on the environment I'd say. Albeit on a different level than whether one should consider killing him- or herself.

And again, I'm merely replying to a statement made above. I'm not telling anyone what to do.